Rename Misc.cpp to CommonFuncs.cpp

Because its only function is declared in CommonFuncs.h.

Source/Core/Common/CommonFuncs.h

@@ -89,5 +89,4 @@ __declspec(dllimport) void __stdcall DebugBreak(void);
 // Generic function to get last error message.
 // Call directly after the command or use the error num.
 // This function might change the error code.
-// Defined in Misc.cpp.
 std::string GetLastErrorMsg();